An asteroid discovered in the 19th century has just been identified as the most crowded we've ever found.
It's known
as 130 Elektra, or just Elektra, and astronomers have recently found that it
has three smaller satellite companions, or moons. This not only makes it the
most abundant asteroid system discovered to date, but it also shows how we can
discover more dim, difficult-to-see asteroid moons in the future.
In their
study, a group of astronomers lead by Anthony Berdeu of Thailand's National
Astronomical Research Institute noted, "Elektra is the first quadruple
system ever identified."
"This
novel finding... demonstrates that specialised data reduction and processing
methods that match the instruments' physics can push their contrast limits even
higher."
It's not
uncommon for asteroids to have smaller companions, albeit they're difficult to
find. Over 150 asteroids out of over 1,100,000 have been discovered to have at
least one moon.
Elektra,
which is about 260 kilometres (160 miles) across, was discovered in the
asteroid belt between Mars and Jupiter in 1873, but its first moon, S/2003
(130) 1, was identified 130 years later, in 2003. S/2014 (130) 1, its second
moon, was discovered in 2014.
There's a
reason why finding these satellites takes so long. At the best of times,
asteroids are small and dimly lighted. Anything much smaller orbiting an
asteroid will be darker, fainter, and potentially significantly outshone by its
parent asteroid.
It will be
more difficult to observe the moon as it becomes smaller and closer to the
asteroid. It's the same reason why it's difficult to spot exoplanets orbiting
other stars up close.
S/2003
(130) 1 is only 6 kilometres in diameter and orbits Elektra at a distance of
roughly 1,300 kilometres; S/2014 (130) 1 is only 2 kilometres in diameter and
orbits Elektra at a distance of around 500 kilometres.
S/2014
(130) 2 is the newly discovered moon, and it's even smaller and closer: only
1.6 kilometres wide with a 340-kilometer average orbital distance. Elektra is
15,000 times fainter than this.
Berdeu and
his colleagues discovered it by running archival data from the SPHERE
instrument on the European Southern Observatory's Very Large Telescope through
a newly built data reduction pipeline that efficiently removed noise from the
original data.
They also
employed data processing methods to model and remove a halo, or prolonged
illumination around the asteroid.
Elektra's
tiny third moon surfaced after the data had gone through these processes.
Despite
the fact that the crew was able to collect some basic information on S/2014
(103) 2, there is still a lot of mystery surrounding its movements around
Elektra. Furthermore, we don't have a lot of data on how these systems form.
The two
moons of an asteroid dubbed Kleopatra were likely produced from dust blasted by
the main body, according to a study published last year, although we don't know
how common this is compared to other creation procedures.
These
could include pebbles being ejected during a collision or minor passing debris
being caught in the asteroid's gravitational field.
Theresearchers said in their report that "the discovery of the first triple
asteroid system marginally opens the path for understanding the mechanisms of
these satellites' genesis."
Furthermore,
their methods could be employed in future studies to discover even more
asteroid moons, which would help to better understand the phenomenon.
References:
- https://doi.org/10.1051/0004-6361/202142623
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